FIG. 1 shows a block diagram of a conventional digital system such as a computer or multimedia system 150 which includes a graphics controller 126 that can support a panel display 132 or an external cathode ray tube (CRT) display 103. It is understood that a typical digital system usually will only include a single display device. However, it is possible to include more than one display in a single system, wherein all of the displays are supported by the graphics controller 126.
In the computer or multimedia system 150 illustrated in FIG. 1, a main control printed circuit board 120, commonly known as the `motherboard`, includes, amongst other devices, a central processing unit (CPU) 122 that is coupled to an address/data bus 124. A graphics controller 126, such as a VGA controller, is also coupled to the bus 124. Once the graphics controller 126 has processed the information necessary for forming an image, the information is coupled to a display bus 128 and then to a first cable connector 130 for supporting the panel display 130.
The motherboard 120 is coupled to the display system 132 via a standard cable 134. The standard cable 134 may include a plurality of pixel data signal lines. The standard cable 134 typically includes 3, 4, 6, 8, 9, 12, 15, 16, 18 or 24 pixel data signal lines. Multiple standard cables 134 may be coupled between the motherboard 120 and the display 132, each having N pixel data signal lines, allowing more pixels to be carried across the cable at one time. Other control signal lines including vertical sync, horizontal sync, pixel clock and data enable lines may be included within the standard cable 134 as well. Power and ground lines may be included within the standard cable 134 as well. If the pixel display 132 is not attached to the computer or multimedia system 150, the power supply lines may be provided separately to the panel display or by a self contained battery source. Exemplary control signal lines are designated as the lines 152, 153 and 154. The standard cable 134 is coupled to the display system 132 via a second cable connector 136. The information received at the cable connector 136 is coupled to the row driver devices (RD1-RDn) 105A-105N (105X) as well as the column driver devices (CD1-CDn) 142A-142N (142X) of the panel display 132. Through the pixel data bus 144, the pixel data is properly sent to each column driver 142X as each row is scanned via row drivers 105X. Techniques of how various panels are scanned is well known in the art and will not be further explained herein. An exemplary display system updates the screen information once every 16 milliseconds. One entire screen image is conventionally called a frame.
An optional CRT display 103 can be coupled external to the computer or multimedia system 150. The CRT display 103 is coupled to the computer or multimedia system 150 and motherboard 120 through a first connector 101, a cable 164, and a second connector 104. The graphics controller 126 generates and drives the analog RGB or digital pixel signals to the CRT display 103 via the bus 123. The analog RGB or digital pixel signals are received across the cable 164 by a CRT driver board 106 which drives the CRT electron guns 107 via a cable 121. Cable 164 may be one of a plurality of cable types having appropriate connectors 101 and 104 to transmit data from the motherboard 120 to the CRT display 103.
In a conventional color display system, the image data necessary to display a single pixel may include 24 bits total, 8 bits each for red, green, and blue. Alternatively, 18 bits total may be used including 6 bits each for the colors red, green and blue as well as other numbers defining a pixel data word including monochrome pixel data words. Video memory 172 is loaded with the data necessary for the graphics controller 126 to instruct the panel display 132 to draw each pixel. Presently, a pixel data word may be sent over the standard cable 134 one pixel at a time in parallel groups of 24 bits or 18 bits, as the case may be, onto pixel data bus 144. Future systems may transfer more than one pixel data word at a time across the standard cable 134, using multiple cables, such that two or more pixels will be transmitted simultaneously.
The column drivers 142X and row drivers 105X are configured to excite predetermined portions of a display screen in one of several known ways. The panel 112 can be a passive matrix LCD display, active matrix LCD display or other type of panel. Optionally a CRT display 103 may be driven alone by the graphics controller 126 as part of a desk-top computer or simultaneously with the panel display 132 that may be a part of a computer or multimedia system 150. Depending upon the display screen being used, appropriate display circuits will be selected. It should be apparent to one of ordinary skill in the art how the column driver circuits 142X and row driver circuits 105X are activated to excite the entire array of pixels within the panel 112 to form a complete image.
As display technology has progressed, skilled practitioners have learned that the quality of a displayed image can change with a variety of parameters including temperature, display voltage linearity and intrinsic properties of the display screen. Because responses to variations in these and other such parameters are known, a system can be optimized to operate for a predetermined known parameter set. Unfortunately, these parameters can change over periods of time as well as environmental conditions. For example, as the time of day changes, the operating temperature of a display system may change. For a computer or multimedia system, the power supply voltage can sag as the battery charge decays between charging periods. It is desirable to compensate for poor image quality of the display, that may be caused by a change in these panel parameters.
Due to market conditions, it is desirable to keep the interface architecture between a CPU and a display fixed as much as possible. It is also desirable to keep the software that controls the interface fixed as much as possible. It is particularly desirable to keep the graphics controller integrated circuit 126 and the video bios fixed, yet improve the controllability of the panel display 132 and the CRT display 103. Typical customers and applications demand that the various components of a personal computer such as a so-called "IBM PC clone" be plug compatible. In other words, changes to the equipment provided by one manufacturer which make a product no longer compatible with equipment manufactured by others, will not readily gain market acceptance. It is therefore desirable to maintain compatibility in the hardware components of a system. For example, it is desirable that any compatible display 132 may be coupled to the motherboard 120 by a standard cable 134.
It is desirable that a display system be manually or automatically modified such that the display image can be improved as operating conditions change. It is further desirable that a system designed to provide these advantages, be compatible with existing software and hardware components such that few changes are required to the existing interface architecture.